Last week we have looked at the very basics of PC defense. However, there are many more things to cover, so I felt that another post in the topic is necessary.

To conclude upon the previous week's topic, having an antivirus software is essential, but many say that having only one antivirus software is not sufficient. A couple years ago I would've agreed, but now I see that many people use an abundance of firewalls, antivirus systems without knowing which one is proper and which one isn't. My advice is that you should have the software I've mentioned in my previous post and nothing else. Windows Firewall is not the best, but it does not mean that it isn't good. Sadly, for some people, good means shiny with a lot of popups so the user can see that "it works". This is not the case.

An antivirus software/firewall/spyware detector works when you see nothing at all and your PC works normally.

Having that cleared up, let's move on to the follow-up section.

Viruses can infect your PC in a number of ways, like so-called "backdoors" that were installed onto your computer by previous malicious programs, but the most common ways are masked links, e-mails (although those are becoming old-fashioned), and vulnerabilities in your browser. Therefore, it is important to get a good browser. Internet Explorer is by far the best... oh God, I can't just write that down with a straight face.

Viruses are the nightmare of any PC user, but they are far less frequent nowadays in a regular environment than it is said.  However, if your computer gets infected with a virus, it is essential for you to clean your PC from them. Also, preventing infections is half a victory, so I'll share some tips about that as well.

Before talking about defense, here is a story about one of the most famous computer viruses:

In 1998, a chinese student, Chen Ing-hau, created the virus named CIH or Chernobyl. The second name was given to the virus because coincidentally, some variants of the virus triggered upon the anniversary of the Chernobyl nuclear accident. It infected over 60 million computers, causing a damage of over 1 billion US dollars. It was one of the most damaging viruses as it could destroy the BIOS (Basic Input-Output System, the "soul" of the computer) which resulted in hardware failure, ergo the people had to buy a new motherboard. It was spreading on various mediums: Yamaha even released CD drives that were infected with the virus.

From this example, we can see that defense against such programs is very important.
Here are the most common types of computer viruses:

Trojan horse

Trojan horse viruses are applications that are usually downloaded by the user. They disguise themselves as useful programs, but they do malicious stuff in the background, for example they steal your data, send your personal information, or just simply destroy some files.

Spyware

These are in relation with the previous category, as the purpose of spyware programs is to send or steal personal data without permission. These are very common, because the user himself often helps these programs to gather data. For example, browsers tend to remember your passwords and usernames, and this offers spyware programs an easy path to steal data. Tracking cookies stored by browsers help viruses to track down your computer's IP address, which can serve as a key to your stored data.

Worms

A computer worm is the "classic" form of the computer virus, spreading over various mediums such as the Internet, local networks, or over portable data storage tools. It multiplies itself and it can cause a huge damage in hundreds of thousands of computers. They are not attached to another program like most viruses.

Keyloggers

These programs are hiding in your PC's memory constantly and they store the keystrokes of your keyboard. This way, they can get access to passwords, bank account numbers and so on if the user types them while the keylogger is active.